An electrical machining apparatus is commonly designed to electroerosively shape a conductive workpiece with a tool electrode in the presence of a machining fluid medium and includes a multiplicity of electrical output means such as a fluid supply unit for pumping the fluid medium into a gap formed between the tool electrode and the workpiece, a power supply for passing an electrical machining current between the tool electrode and the workpiece across the fluid-filled machining gap to electroerosively remove material from the workpiece and a drive unit for relatively displacing the tool electrode and the workpiece to advance the material removal in the workpiece. All such electrical output means are commonly designed to be energized from a single input source of electric power for performing their respective operating functions. Thus, when a power failure happens to occur or a power shut-off needs to be exercised, these multiple electrical output means are deenergized simultaneously. Upon recovery of electric power after the failure or shut-off in the input source, it has been the conventional design that these multiple output means are simply arranged to follow the power recovery.
It has now been recognized that such conventional arrangement has been a major source of difficulties which prevent the machining apparatus from performing a given machining operation efficiently and on a full automatic basis. With all the multiple electrical output means allowed to start driving at the same time, the power input may be deficient to permit each individual output means to start operating normally or without undue delay in restoring the normal operating mode.